Mobile equipment is often battery powered so that it can be moved to any location and used without the need of an electrical power outlet. One such device, for example, is a battery powered mobile x-ray device (BPMXD) which is moved from patient-to-patient throughout the hospital such as, for example, in emergency, intensive care, pediatrics and surgery. Such units must always have enough battery capacity available to produce a diagnostically useful x-ray, and if it is self-propelled, enough capacity to return the unit to its recharging station.
Battery powered medical equipment requires some means for indicating the remaining battery capacity. Typically, this takes the form of a percent full gauge or display based on battery voltages, which indicates the approximate state-of-charge of the battery. The battery voltage drops very little over much of the battery's usable capacity, and drops linearly over an even smaller portion of its usable capacity. Consequently, this method of indicating battery capacity is not reliable. However, to be useful, radiological technicians would like to know how many patient exams the percent capacity display represents.
One solution considered is to simply change the "battery capacity remaining" display to "PATIENT EXAMS REMAINING". However, this would not be practical, since all BPMXD's are used differently. For example, one hospital may park a BPMXD in one location but travel throughout the hospital to do patient exams. This BPMXD would use a substantial amount of battery capacity for each patient exam. Another BPMXD may be located in a surgery room and for sterile reasons never leave that room. This particular BPMXD would use very little battery capacity for each patient exam.
It would be desirable then to have a means for implementing a "PATIENT EXAMS REMAINING" (PER) feature, indicating the patient exams remaining before battery capacity is exhausted, in any BPMXD that has the capability of monitoring battery capacity usage as well as displaying PER. Furthermore, it would be desirable for the PER function to be capable of operating properly for a wide range of usage.